Nitrous oxide emissions from two dairy pasture soils as affected by different rates of a fine particle suspension nitrification inhibitor, dicyandiamide

In grazed pasture systems, a major source of N2O is nitrogen (N) returned to the soil in animal urine. We report in this paper the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), applied in a fine particle suspension (FPS) to reduce N2O emissions from dairy cow urine patches in two different soils. The soils are Lismore stony silt loam (Udic Haplustept loamy skeletal) and Templeton fine sandy loam (Udic Haplustepts). The pasture on both soils was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Total N2O emissions in the Lismore soil were 23.1-31.0 kg N2O-N ha(-1) following the May (autumn) and August (late winter) urine applications, respectively, without DCD. These were reduced to 6.2-8.4 kg N2O-N ha(-1) by the application of DCD FPS, equivalent to reductions of 65-73%. All three rates of DCD applied (7.5, 10 and 15 kg ha(-1)) were effective in reducing N2O emissions. In the Templeton soil, total N2O emissions were reduced from 37.4 kg N2O-N ha(-1) without DCD to 14.6-16.3 kg N2O-N ha(-1) when DCD was applied either immediately or 10 days after the urine application. These reductions are similar to those in an earlier study where DCD was applied as a solution. Therefore, treating grazed pasture soils with an FPS of DCD is an effective technology to mitigate N2O emissions from cow urine patch areas in grazed pasture soils.